Numerical Control drilling machines used for the drilling of printed circuit boards (PCBs) hold very tight tolerances in the X, Y and Z axes. The means of controlling the Z-axis drill depth is to use a drill bit with a plastic collar which has been coaxially positioned on the drill bit a predetermined distance from the drill tip. If this distance is set incorrectly, the depth of the drilled holes becomes incorrect and the quality of the PCB deteriorates.
The plastic collar is positioned on the drill bit by means of a mechanical plunger mechanism. The drill bit is first inserted into a holder. The operator then applies a force to a lever to activate the plunger and slide the plastic collar to the desired position. The plunger mechanism is calibrated periodically to attempt to maintain the collar's position within allowed tolerances. However, once the collar is so positioned on the drill bit, there is no method available to periodically verify the validity of the collar's position.
Accordingly, it is the object of the present invention to provide a novel test device which can be utilized to verify the longitudinal position of a collar coaxially mounted on a drill bit.